In recent years, many portable electronic devices such as combination cameras (videotape recorder), mobile phones, and portable computers have been introduced, and their size and weight have been reduced. Accordingly, as a portable power source for the electronic devices, batteries, in particular secondary batteries have been actively developed. Specially, lithium ion secondary batteries have attracted attention as a battery capable of realizing a high energy density. For the battery, which is thin, is flexible, and has a shape with a high degree of freedom, many researches have been made.
For such a battery having a shape with a high degree of freedom, all solid-state polymer electrolyte in which an electrolyte salt is dissolved in a polymer compound, a gelatinous polymer electrolyte in which an electrolytic solution is held in a polymer compound or the like is used. Specially, since the gelatinous polymer electrolyte holds an electrolytic solution, the contact characteristics with an active material and the ion conductivity are superior compared to the all solid-state polymer electrolyte. Further, the gelatinous polymer electrolyte produces less liquid leakage than the electrolytic solution. Therefore, the gelatinous polymer electrolyte has attracted attention.
For high molecule used for the gelatinous polymer electrolyte, researches have been made for various materials such as an ether high molecule, methyl methacrylate, and polyvinylidene fluoride. Of these materials, there are high molecules using polyvinyl acetal such as polyvinyl formal and polyvinyl butyral.
For example, in Patent documents 1 and 2, the ion conductive solid composition of matter using polyvinyl butyral is described. In Patent document 3, the gelatinous electrolyte containing polyvinyl formal and an electrolytic solution is described. Further, in Patent document 4, the gelatinous electrolyte in which the amount of the electrolytic solution is increased by adjusting the content of the hydroxyl group in polyvinyl formal is described. Furthermore, in Patent document 5, the gelatinous electrolyte using an epoxy cross-linking agent and a catalyst is described.    Patent document 1: Japanese Unexamined Patent Publication No. S57-143355    Patent document 2: Japanese Unexamined Patent Publication No. S57-143356    Patent document 3: Japanese Unexamined Patent Publication No. H03-43909    Patent document 4: Japanese Unexamined Patent Publication No. 2001-200126    Patent document 5: U.S. Pat. No. 3,985,574